1. Technical Field
The present invention relates generally to an apparatus and process for making hollow tapered tubes. More particularly, the present invention is an apparatus and process which identifies, achieves, and maintains position control during the roll forming process. Specifically, the present invention is an apparatus and process which uses feedback systems to control roll positioning cylinders at different ratios of displacement thereby best accommodating machinery geometry and various shaft taper rates.
2. Background Information
Metal tapered tubes have been used for decades in numerous pole applications including for supporting lamps as used for illuminating highways, roads, streets, developments, parking lots, and other public areas. These metal tapered tubes have been particularly adopted for use on all major highways and roadways and most particularly in city or urban areas as illuminated roadways and public areas such as parking lots are much safer than non-illuminated ones. These tapered tubes have also been used in other applications including as cable poles, electrical wire poles, flag poles, etc. and are therefore very popular with urban planners, civil engineers, architects, city engineers, etc.
These metal tapered tubes are further very popular for various reasons. First, these metal tubes have a pleasant appearance due to the metallic properties, tapered shape, and general long life. Second, these metal tubes are of a very high strength due to the high strength of metal and the tapered shape. Third, these metal tubes are light weight due to the hollow nature combined with the physical properties of metal which include high strength without large mass or thickness.
In the past, the tubes were often not tapered and instead were manufactured as a cylinder due to the ease of such manufacturing processes. However, the tapered design offers so many advantages including improved strength that it is the overwhelming choice in numerous tube uses including illuminated light poles.
In the past, metal tapered tubes have been produced or formed from a metal plate that has been cut in advance. The metal plate is generally cut in a regular trapezoidal shape or a shape also referred to as a section of a frustrum of a right circular cone, that is the two ends are parallel although one is longer than the other, while the two sides are the same length but angled toward each other.
This metal plate is passed through a peripheral curved surface formed by a group of rollers arranged on the same periphery to press the metal plate with many contact points or surfaces. The resiliency of the metal plate is utilized to force the metal by forming into a different shape, in this case from a flat body into a curved body that is preferably curved in a circular cross sectional manner. All of this occurs by advancing the plate through the group of rollers while simultaneously withdrawing said group of rollers in a continuous radial and proportional manner. After this process, the product is finished by welding and finishing the joints.
One example of such prior art practice is found in U.S. Pat. No. 3,361,319 issued to Masao Sato et al. As is shown in FIGS. 4a and 4c, the six rollers are continuously withdrawn as the cut plate is pushed through thereby forming a tapered tube. In this and other prior art arrangements, the system is always physically geared, linked or cammed to position the working rolls during the process where in each scenario the position of the working rolls is always determined by fixed mechanics and the motion of the machinery. For instance, in the '319 patent, the position of the rollers is determined and controlled by a rotatable cam plate. In effect, the withdrawing motion of the rollers from a central axis is identical for each roller and is a fixed equation, specifically, a fixed linear equation based upon the motion of the machinery as physically connected to the withdrawing apparatus on each roller.
As each piece of metal is not uniform, and the forming of each flat metal plate into a curved and circular cross sectioned tube is never uniform, the process of withdrawing each cylinder uniformly along the length of the tube being formed and uniformly as each roller withdraws by the same radial distance is a quite imperfect process. Often the metal plate twists, bends, contorts, etc. as it is formed. The current processes have no way of addressing this nonuniform forming. As a result, a need exists for monitoring and/or identifying current locations and status of the metal plate and rollers during the process, and then achieving and maintaining proper corrections in each roller withdraw rate and location, all of which must remain independent of the other rollers withdraw rate and location although correlated to assure that the cumulation of all of the rollers withdraw rate and location is maximized to achieve the optimal forming and thus most uniform formed tapered tube or pole shaft.
In addition, current forming processes merely run the flat metal plate through one former resulting in a substantially tapered tube with a pair of spaced apart edges that need welded together. The resiliency of the metal is such that the forming step cannot in one pass form a flat metal into a circular cross section and instead provides a C-shaped element in which the spaced apart edges must be forced together during welding. This forcing is negative. Furthermore, due to the current inaccurate forming as described above, the edges are not always parallel, are often too far apart, are often not in the same plane, are often twisted over the length of the tube, etc. whereby welding is either ineffective or less than optimal.
For these and other reasons that are known to those skilled in the art, a new and improved apparatus and process is needed to manufacture metal tapered tubes for pole shafts such as those for use in illuminating streets, roads, parking lots, highways, and other applications.